Lids which provide pressure relief venting of a container are used to seal containers holding material, especially liquids, which must be maintained at or below a desired pressure. Such lids have found widespread application in regulating the internal pressure of containers typically containing hazardous liquids which may be inflammable, volatile, acidic or even highly caustic.
As the number of containers carrying hazardous material being transported has increased, the desire to prevent environmentally damaging spills has led to the further development of lids which can provide pressure relief venting while also maintaining a fluid-tight seal when the container is dropped or collides with another object. These lids usually have a cover urged by a spring member against the container for sealing the container opening and maintaining the seal while being able to withstand a hydraulic shock of contents within the container impacting against the cover, yet allowing the seal to be broken to regulate pressure within the container.
A prior commonly known pressure relief venting lid has a substantially flat, generally circular port cover which is attached to a cross-arm supported by a piston. The piston is attached at one end to the center of the cover and at the opposite end to the cross-arm to urge the cover into sealing engagement over the container opening when the cover is secured over the opening. Typically, the cross-arm is hingedly mounted to allow the cover to be moved away from the opening to provide access to the interior of the container and may be clamped down when the cover is sealing the opening to support the cover. A finger extending from the cross-arm may be provided for engaging the cover to prevent the cover from rotating and unscrewing from the piston during use.
Unfortunately, while these lids may be designed to maintain a fluid-tight seal when subjected to the hydraulic shock of a short container drop, large bending moments created around the centrally located piston from liquid impacting the vent cover can cause the cover to unseat and spill contents from the container. Even worse, when exposed to a more severe shock, such as when a container is dropped from an even greater height, for example, of two feet or higher, these flat port covers tend to permanently deform thereby increasing the likelihood of an environmentally contaminating spill and typically rendering the lid unusable. Furthermore, these lids are ill-suited for complying with recent regulations which are more stringent, requiring a pressure relief venting lid secured to a container holding material having a specific gravity of 1.2 to survive a container drop of four feet while maintaining a fluid-tight seal.
Another problem with the aforementioned lids is that the top of the port cover is generally exposed and unprotected which can allow direct contact between the cover and another object during an accident possibly damaging the cover and/or causing a spill. This exposed design is also undesirable since it can allow escaping pressurized vapor to directly contact and injure a nearby worker during pressure relief venting or when the lid is being opened.